Over the years a variety of material dispensers have been developed including those directed at dispensing foamable material such as urethane foam. For example, when certain chemicals are mixed together they form polymeric products while at the same time generating gases such as carbon dioxide and water vapor. If those chemicals are selected so that they harden following the generation of, for example, carbon dioxide and water vapor, they can be used to form “hardened” (e.g., a cushionable quality in a proper fully expanded state) polymer foams in which the mechanical foaming action is caused by the gaseous carbon dioxide and water vapor leaving the mixture.
In some techniques, synthetic foams are formed from liquid organic resins and polyisocyanates in a mixing chamber (e.g., a liquid form of isocyanate, which is often referenced in the industry as chemical “A”, and a multi-component liquid blend such as one including polyurethane resin for producing polyurethane foam, which is often referenced in the industry as chemical “B”). The mixture can be dispensed into a receptacle, as in a package or a foam in place bag (see e.g., U.S. Pat. Nos. 4,674,268, 4,800,708 and 4,854,109 which are incorporated by reference), where it reacts to form the foam.
A particular problem associated with certain foams as in polyurethane foams is that once mixed, the organic resin and polyisocyanate generally react relatively rapidly so that the resultant foam product tends to accumulate in all openings through which it passes, including a backing up of foam into openings through which the components passed before mixing. Furthermore, some of the more useful polymers that form foamable compositions are adhesive. As a result, the foamable composition, which is often dispensed as a somewhat viscous liquid, tends to adhere to objects that it strikes and then harden in place. Many of these adhesive foamable compositions tenaciously stick to the contact surface making removal particularly difficult.
Solvents are often utilized in an effort to remove the hardened foamable composition from surfaces not intended for contact, but even with solvents (particularly when considering the limitations on the type of solvents suited for worker contact or exposure) this can prove to be a difficult task. The undesirable adhesion can take place in the general region where chemicals A and B first come in contact (e.g., a dispenser mixing chamber) or an upstream location as in individual injection ports in light of the expansive quality of the mix, or downstream such as a dispensing gun or, in actuality, anywhere in the vicinity of the dispensing device upon, for instance, a misaiming, misapplication or leak (e.g., a foam bag with leaking end or edge seal). For example, a “foam-up” in a bag dispenser, where the mixed material is not properly confined within a receiving bag, can lead to foam hardening in every nook and cranny of the dispensing system making complete removal not reasonably attainable particularly when considering the configuration of the prior art systems. A misdirected stream from a hand held gun outlet can also end up covering numerous unwanted surfaces.
Because of this adhesive characteristic, steps have been taken in the prior art to attempt to preclude contact of chemicals A and B at non-desired locations as well as precluding the passage of mixed chemicals A/B from traveling to undesired areas or from dwelling in areas such as the discharge passageway used in aiming the A/B chemical mixture. Examples of injection systems for such foamable compositions and their operation are described in U.S. Pat. Nos. 4,568,003 and 4,898,327, and incorporated entirely herein by reference. As set forth in both of these patents, in a typical dispensing cartridge, the mixing chamber for the foam precursors is a cylindrical core having a bore that extends longitudinally there through. The core is typically formed from a fluorinated hydrocarbon polymer such as polytetrafluoroethylene (“PTFE” or “TFE”), fluorinated ethylene propylene (“FEP”) or perfluoroalkoxy (“PFA”). Polymers of this type are widely available from several companies, and one of the most familiar designations for such materials is “Teflon”, the trademark used by DuPont for such materials. For the sake of convenience and familiarity, such materials will be referred to herein as “Teflon”, although it will be understood that the materials available from companies other than DuPont and of other types can also be used if otherwise appropriate.
In the aforementioned systems, a plurality of openings (usually two) are arranged in the core in communication with the bore for supplying the organic resin and polyisocyanate to the bore, which acts as a mixing chamber. A combination valving and purge rod is positioned to slide in a close tolerance, “interference”, fit within the bore or mixing chamber to control the flow of organic resin and polyisocyanate from the openings into the bore and the subsequent discharge of the foam from the cartridge.
With hand held and foam-in-bag dispensing apparatus there is typically provided chemicals A/B from their respective sources (typically a large container such as a 55 gallon drum for each respective chemical) in the desired state (e.g., the desired flow rate, volume, pressure, and temperature). Thus, even with a brand new dispenser, there are additional requirements involved in attempting to achieve a desired foam product. Under the present state of the art a variety of pumping techniques have arisen as in individual pumps designed for insertion directly into the chemical source containers coupled with a controller provided in an effort to maintain the desired flow rate characteristics through pump control.
FIG. 1 illustrates an (electric) hand held two component prior art dispensing system 20. System 20 includes chemical drums 22, 24 for the two chemical components “A” and “B” to be mixed to produce a dispensed foam. Pumps 26, 28 extend within the drums “A” and “B” each pump having a combination tachometer and a DC motor set (27, 29). Pumps 26, 28 are each wired to control console 30. Chemical conduits 32, 34 extend from the pumps, through hanging support structure 36 and are connected to hand held dispenser 38. Heater wire coils are present in each of conduits 32, 34, to control chemical temperature, and electric lines 31, 33 extend from the control console and into electrical connection with the heater wire coils in the conduits. Electric line 35 extends from the control console to the electric valve rod reciprocation motor of the dispenser. Adjacent dispenser 38, there is positioned stand 40 for supporting box 42 and a dispenser holster 44. Dispensing system 20 is a closed loop control system with positive displacement pumps which attempt to maintain “on ratio” delivery for every dispenser “shot” activation by continuously monitoring and adjusting temperature, pressure and pump speed.
FIG. 2 provides an exploded view of prior art hand held dispenser 38 which comprises handle 46 having hand grasp extension 48 and mounting base 50 supporting valve rod reciprocation motor 52, mixing cartridge “below” carrier 54 and mixing cartridge “upper” carrier 56. Carriers 54 and 56 are design to retain in position mixing cartridge assembly 58. Lower carrier 54 also functions as a manifold for chemicals received via hose adaptor fittings 60, 62 and receives valve control plugs 64, 66, filter assemblies 68, 70, and O-rings 71, 73 for avoiding chemical leakage between the lower carrier outlet (72 one shown) and cartridge assembly's housing ports (74—one shown). Chemical mixing cartridge 58 is clamped between lower carrier 54 and upper carrier 56, which are secured together by fasteners 76, while cartridge position fixation screws 78 extend into fixing cavities 80, in 80′ cartridge assembly 58.
FIGS. 3A and 3B provide an illustration of the interior of prior art mixing cartridge assembly 58 (see U.S. Pat. No. 4,898,327 sharing similarities with that shown in FIG. 2. As shown, the prior art cartridge assembly 58 includes housing 82 with accessible rear end 84 (C-Clip), apertured front end 86, Teflon mixing chamber 88 which defines chemical mixing area 89 (the actual “mixing chamber”), chemical A and B mixing chemical port members 90, 92 (FIG. 3B) receiving chemical from housing port inlets 91, 93, and valve rod 94. In an effort to maintain a sealing relationship with the valve rod, Belleville washer stack 96 pushes against the intermediate disk 98 to maintain the Teflon material compressed. After packing, the open rear end is closed by way of a special pressing tool (not shown) which allows for the end cap 91 and clip 84 to be positioned.
Despite a great deal of effort in the art (e.g., see, for example, U.S. Pat. Nos. 4,469,251; 4,867,346; 5,211,311; 5,090,814; 5,180,082; 5,709,317) the prior art mixing cartridges need to be serviced and replaced with a great deal of frequency causing a corresponding large amount of wasteful operator down time and operator frustration.
In these prior art devices the actual mixing takes place in the cylindrical hole or cavity that is drilled through the central axis of the Teflon cylinder. Thus, the mixing region chamber is actually a hole surrounded by the inside diameter of the relatively thick walled Teflon cylinder (it is noted that the term “mixing chamber” is often used in the art in a broader sense, to include the chamber forming structure). The cavity or bore is where both urethane components A and B impinge, mix, and start the reaction process that creates foam.
Functional prior art foam-dispensers that employ a Teflon mixing chamber such as those listed above are customarily made from various grades of Teflon, because of its superior non-stick properties. The mixing chambers such as those in the patents noted above are generally cylindrical in shape and compressed against the front of the housing. Desirable features of a mixing chamber in most settings include, (i) maximizing mixing efficiency; (ii) providing a laminar output stream; (iii) providing leak free valving in the chemical flow.
The mixing chambers of the prior art are generally designed to provide mechanical support to impingement ports used to aim the chemical being ejected. One purpose of these chemical ports is to focus the flow of liquid precursors for high impingement velocity in an effort to enhance efficiency. The nozzles that the chemicals pass through just prior to entering the mixing chamber itself are commonly called ports in the industry. These ports help to minimize the cross-sectional area of the output jet, maximizing flow velocity, and thereby maximizing impingement pressure when the two streams collide. The exit diameter of the port nozzle opening is designed in these systems with an understanding the opening should not to be smaller than the pressure output capacity of the pumping system (e.g., 200 to 300 psi range which might be deemed a comfortable operational level, with a 400 to 500 psi range being representative of a practical prior art system maximized pressure level). Mixing can possibly be enhanced by using additional mechanical mixing elements in the system, but these can add significant complexity to the design, which can often outweigh any possible mixing advantage.
For greater efficiency (and foam quality), maintenance of both ports clean and unobstructed allows for retention of initial production settings. Maintaining the ports properly aligned to impinge at the desired location as in the centerline of the mixing chamber is also generally considered as being desirable under the prior art systems.
With respect to a laminar output stream, the length of the mixing chamber channel provides a means of damping the turbulence of the chemical flow immediately after impingement. If the turbulence is properly damped there is provided a laminar quality to the flow of (mixed) chemical that exits the reception (mixing) chamber. A laminar output flow, commonly called a “pencil pour”, is easier to aim and much cleaner to work with than a turbulent or spinning output stream. If the mixing chamber length to diameter ratio is too small, however, the output stream can be highly erratic. This can be messy for the operator, and is an indication that the chemicals are badly mixed.
Also, it is generally believed in the industry that mixing can be improved in systems having a longer dwell time in the confines of a mixing chamber as the confinement helps keep the chemical components in close proximity for a longer time. On the other hand, if the mixing chamber is too long, the axial force required to retract the valving rod increases significantly, resulting in an increase in the size and weight of the associated drive mechanism. High weights and large size requirement are generally unacceptable for practical application in, for example, hand held packaging systems (e.g., the weight of a hand held dispenser needs to be maintained low for user comfort).
Another source for the development of a non-laminar or erratic flow in prior art systems is having the chemicals not impinge at the geometric centerline of the mixing chamber inside diameter, in that rotational momentum can be imparted to the flow stream in the aforementioned prior art systems. This rotational momentum can manifest itself in a spinning of the output stream, which appears as a spray pattern and can cause various problems.
The mixing chamber in most systems also provides a means for the valving rod to shut off the flow of liquid precursors and to open up to allow flow and mixing to occur. Thus, an effort is made in prior art systems to maintain valve arrangements that avoid the formation of highly problematic leak paths that can allow the A chemical to mix with the B chemical at undesirable times and locations. Since Teflon is a marginal sealing material, however, it is quite difficult to provide the necessary sealing in the pressure range of typical interest (e.g., 200 to 500 psi). Compression of the Teflon can potentially improve its function as a seal. For example, compression with a psi loading three to four times greater than the fluid pressure being sealed. A stack of Belleville washer at the back of the housing has been used to provide this load.
Also, Teflon seals have the potential for improving with time under load, as over time the Teflon material can cold-flow into the microscopic surface imperfections that are potential leak paths along the face of a sealing surface. Teflon material has more cold-flow tendency than most other engineering plastics because the polymer strings that comprise the material do not stick to each other. Because of this, areas of Teflon material are free to slide past each other, to an extent greater then most other engineering plastics, making Teflon material a useful non-stick surface.
While this cold flow distortion of the Teflon can be beneficial (e.g., allowing for the conformance of material about surfaces intended to be sealed off) it is also a cause of several problems, including the potential for the loss of the fit between the bore and the valving rod as well as the fit between the openings (e.g., ports) through which the separate precursors enter the bore for mixing and then dispensing. In many of the prior art systems utilizing Teflon, the Teflon core is fitted in the cartridge under a certain degree of stress in order to help prevent leaks in a manner in which a gasket is fitted under stress for the same purpose. This stress also encourages the Teflon to creep into any gaps or other openings that may be adjacent to it which can be either good or bad depending on the movement and what surface is being contacted or discontinued from contact in view of the cold flow.
Under these prior art systems, however, over time the sealing quality of the core is lost at least to some extent allowing for an initial build up of the hardenable material which can lead to a cycle of seal degradation and worsening build up of hardened material. This in turn can lead to a variety of problems including the partial blockage of chemical inlet ports so as to alter the desired flow mix and degrade the quality of foam produced. In other words, in typical injection cartridges the separate foam precursors enter the bore through separate entry ports. Polyurethane foam tends to build up at the area at which the precursor exits the port and enters the mixing chamber. Such buildups cause spraying in the output stream, and dispensing of the mixture in an improper ratio. The build up of hardened material can also lead to partial blockage of the dispenser's exit outlet causing a misaiming of the dispensed flow into contact with an undesirable surface (e.g. the operator or various nooks and crannies in the dispenser).
The build-up of hardened/adhesive material over time leads to additional problems such as the valve rod becoming so adhered within its region of seal/no-seal reciprocal travel that either the driver mechanism is unable to move the rod (leading to an oft seen shut down signal generation in many common prior art systems) or a component along the drive train breaks off which is often the valve rod engagement location relative to some prior art designs. Moreover, if the Teflon sealing element is forced to move after it has set at a given position, the quality of sealing, as explained in greater detail below, will be degraded until the Teflon can re-set in the new position.
A disruption of any of the above mixing chamber functions will necessitate service or replacement of the mixing module, with resultant downtime, inconvenience, and expense. Anything that can eliminate or reduce the occurrence of these problems will greatly enhance the reliability of the mixing module.
As a result of studying the aforementioned problems and difficulties associated with the prior art, the inventors have come to the belief that a source of many of the difficulties and problems associated with the prior art devices is the tendency for the mixing chamber to move within the mixing chamber housing. A review has thus been made under the present invention as to the tendency for the chamber to “move around” within the confining cylinder of the mixing chamber housing. The effects of this movement has been observed by the changes in the position of the stainless steel chemical ports of prior art devices (e.g., by looking through the two flow holes that are drilled radially through the outer metal housing). These housing inlet holes provide a clear view of the chemical ports that are located radially in the body of the Teflon mixing chamber. It has been observed that after a few thousand cycles, the ports will usually rotate noticeably with respect to the mixing chamber housing inlet holes and that the shifting tends to get worse with more cycles. This movement problem has been determined to manifest itself in mixing chamber movements in both an axial and a radial direction.
Some examples of the problems considered to exist as a result in the shifting of the mixing chamber within its housing unit, include:
I. Movement of Chemical Ports from Ideal Position                a. Shifting of the mixing chamber, even by a small increment, causing the ports to move out of their ideal (as designed and assembled) position.        b. If the A and/or B chemicals ports move out a desired impingement position, foam quality can be affected.        c. The output stream of reacted chemicals from the exit of the mixing module may spray due to a rotation in the output stream caused by the ports being out of position.        d. If the rotation is severe, the ports can move to a position so far out of alignment with the flow holes in the housing, that the flow of chemical can be severely restricted, and system shutdown will result.        
II. Chemical Leakage                a. Shifting of the mixing chamber, even by a small increment, can seriously degrade its sealing ability, causing leaks of A and/or B chemical to locations where they can mix and react with each other and cause various problems.        b. Leaks that cause urethane deposits near the exit areas of the chemical ports can cause the output stream of the mixing module to spray, or even total flow blockage.        c. If a leak is large enough, it can lead to what is known as a massive crossover, where large amounts of urethane are produced in the A and/or B-sides of the dispenser manifold. Massive crossover in a dispenser manifold are difficult to clean, and often result in the replacement of many expensive components.        d. Chemical leaks can also cause the valving rod to bond to the mixing chamber. The urethane that forms on the inside diameter of the mixing chamber over time will have a tendency to jam a prior art mechanism. Wherein the drive mechanism can no longer move the rod, causing a sensed system shut down or an equipment breakdown as in a broken rod connector.        e. Chemical leakage into a solvent source such as a solvent chamber found in a rear of a mixing module, reduces the effectiveness of the solvent, and greatly reduces the life of the mixing module.        
III. Premature Wear of the Mixing Chamber                a. Most mixing modules are based on relatively tight tolerances and fairly critical press fits. Thus, any tolerance deviation caused by movements leakage, can lead to related failures.        b. If these fits are not held, the mixing chamber, will, in addition to leaking, also, be subjected to damage due to motion of the valving rod. The damage may not be noticeable to the eye, but even microscopic deformations can have noticeable effects.        c. Any damage or wear to the Teflon mixing chamber will exacerbate the leakage issues noted above.        d. Damage to the inside diameter surface of the mixing chamber will also create fissures, crevices, and score marks that will be nucleation sites for urethane buildup. Once the urethane buildup gets started, it will attract more urethane to itself, growing in size until it causes a mixing module failure.        
The sequence of events is considered under the present invention to be as follows (although it is not the intention under the present invention to be specifically bound or limited in any fashion in the beliefs (e.g., analysis and conclusions) described herein in development of the present application) with the explanation given relative to a typical prior art embodiment using Bellville washer compression:                1. The mixing module starts its life in aligned condition, with the ports in the mixing chamber in good alignment with the through holes in the mixing module housing. As the mixing module is used, urethane naturally builds up on the inside diameter of the mixing chamber.        2. The slow buildup of urethane on the inside diameter of the mixing chamber gradually increases the sticking force between the valving rod and the mixing chamber.        3. At some point, when the bond strength increases to a critical level, the act of retracting the valving rod causes the mixing chamber to move back into the Belleville washers that constrain it from the rear. The stack of Belleville washers is in effect a powerful spring with short travel.        4. The valving rod will move the chamber in the direction of travel, which compresses the Belleville stack. This will increase the force pushing the mixing chamber forward until the urethane bond is broken between the mixing chamber and the valving rod.        5. Once the bond is broken, the Belleville washer forces the mixing chamber forward, to near its original position.        6. If all of this motion were “perfect”, the mixing chamber would not rotate, and it would return to its original position. However, the forces in this situation are considered not perfectly balanced, and the mixing chamber tends to rotate as it is pulled back, or as it seeks to return to its home position.        7. The mixing chamber tends to rotate a tiny amount with each cycle. After a large number of cycles, the sum of these minute rotations manifest as a significant change in the radial position of the port inside the mixing chamber housing.        8. These stresses on the chamber also cause it to distort, which may account for the port movement that is apparent in the axial direction with respect to the housing flow holes.        
An additional problem associated with the prior art is the difficulty to gain access to the mixing chamber to correct any of the above noted problems that arise. For example, as seen from FIGS. 3A and 3B, prior art mixing modules, have been assembled using clip rings on the back cap or compression cap. In order to install the clip ring, the back cap is forced into the Belleville washer stack, an action that requires about 200 lbf to accomplish. Thus, the prior art method of assembly requires the use of machines like arbor presses and some special holding and alignment fixtures to put the prior art mixing module together. This type of design is difficult to both assemble and disassemble, as the clip ring can be both difficult to install and to remove with the heavy loads involved.
An additional problem associated with the prior art designs featuring an integrated front end cap of the housing is the tendency for the front end cap to deform or bulge out due to the loads exerted by the Belleville washer stack on the mixing chamber and, in turn, on the front end cap abutting the mixing chamber. The prior art front cap swaged onto the housing design is not of particularly high strength and is subject to deformation. This deformation can generate reliability problems and lead to problems as outlined above for when the mixing chamber shifts in position.
The prior art designs also suffer from difficulty in assembly. For example, the typical assembly process includes inserting the mixing chamber from the back end and attempting to line up the chemical ports prior to adding the Bellville washers, compression cap and C-clip. This alignment can be difficult and even if properly achieved the activity associated with locking the C-clip can easily result in misalignment problems. In such events, the user has to undergo a difficult C-clip removal and alignment sequence. The difficult disassembly and assembly also renders prior art devices poorly suited for field repairs and field rebuilds, requiring, instead, return to a service facility and service technician involvement.
An additional problem associated with the prior art design, is the difficulty in properly filling the solvent chamber with solvent. If can be an awkward and messy procedure to fill prior art mixing modules with solvent. For example, under one prior art design the solvent has to be dispensed into the back of the mixing module, just prior to using an arbor press to compress the washers. In additional to spillage during this process it is difficult to know whether the mixing module is sufficiently full of solvent (e.g., because the viscosity of most solvent relied upon is quite high at room temperature it is easy for air to become trapped in the mixing chamber, giving a false impression of a full solvent fill). Once assembled, a check of the solvent cannot be made under the prior art design absent going through the difficult dissembling process. Considering that mixing module life is typically proportional to solvent quantity, the presence of trapped air and low quantity solvent levels can seriously degrade the life of the mixing module.
Once assembled and the C-clip locked, the solvent inside can degrade or degrade internal seals over time. Thus rendering the prior art design ill suited for harsh climates and/or prolonged storage as often involved with military applications.